The broad objectives of this research proposal are to increase basic knowledge of response of tumor tissue to irradiation and to evaluate quantitatively, carefully selected means of modification of tumor response vis a vis normal tissue. Two fundamental parameters of response to be studied in detail are: Recurrence time distribution and pattern of regression. The latter is to be examined for a correlation with probability of recurrence. A major interest will be the evaluation of the role of host reaction to treatment with Corynebacterium parvum to affect tumor growth and to modify response to irradiation. These projects are planned to be based upon two tumor systems: Mammary carcinoma (essentially non-immunogenic) and fibrosarcoma (definitely immunogenic). Further, a special feature of these experiments will be an examination for a correlation between histological features of the individual tumor (especially character of cellular infiltration) and response (in normal and C. parvum treated animals). Also, the plan is to complete the work started upon hyperthermia as an anti-tumor agent and a modifier of radiation response. The intention is to develop the capability of quantitative culture of primary explants of fibrosarcoma for tumor cell survival studies. This will be especially valuable in the C. parvum project but would obviously be an important tool in many studies of tumor radiation biology.